Helveg Stig, López-Cartes Carlos, Sehested Jens, Hansen Poul L, Clausen Bjerne S, Rostrup-Nielsen Jens R, Abild-Pedersen Frank, Nørskov Jens K
Haldor Topsøe A/S, Nymøllevej 55, Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
Nature. 2004 Jan 29;427(6973):426-9. doi: 10.1038/nature02278.
The synthesis of carbon nanotubes with predefined structure and functionality plays a central role in the field of nanotechnology, whereas the inhibition of carbon growth is needed to prevent a breakdown of industrial catalysts for hydrogen and synthesis gas production. The growth of carbon nanotubes and nanofibres has therefore been widely studied. Recent advances in in situ techniques now open up the possibility of studying gas-solid interactions at the atomic level. Here we present time-resolved, high-resolution in situ transmission electron microscope observations of the formation of carbon nanofibres from methane decomposition over supported nickel nanocrystals. Carbon nanofibres are observed to develop through a reaction-induced reshaping of the nickel nanocrystals. Specifically, the nucleation and growth of graphene layers are found to be assisted by a dynamic formation and restructuring of mono-atomic step edges at the nickel surface. Density-functional theory calculations indicate that the observations are consistent with a growth mechanism involving surface diffusion of carbon and nickel atoms. The finding that metallic step edges act as spatiotemporal dynamic growth sites may be important for understanding other types of catalytic reactions and nanomaterial syntheses.
具有预定义结构和功能的碳纳米管的合成在纳米技术领域起着核心作用，而抑制碳的生长对于防止用于氢气和合成气生产的工业催化剂失效是必要的。因此，碳纳米管和纳米纤维的生长已得到广泛研究。原位技术的最新进展现在为在原子水平上研究气固相互作用开辟了可能性。在此，我们展示了通过时间分辨、高分辨率原位透射电子显微镜对负载型镍纳米晶体上甲烷分解形成碳纳米纤维的观察。观察到碳纳米纤维是通过镍纳米晶体的反应诱导重塑而形成的。具体而言，发现石墨烯层的成核和生长由镍表面单原子台阶边缘的动态形成和重构所辅助。密度泛函理论计算表明，这些观察结果与涉及碳和镍原子表面扩散的生长机制一致。金属台阶边缘作为时空动态生长位点这一发现对于理解其他类型的催化反应和纳米材料合成可能很重要。
